Sonar systems are used to detect, navigate, track, classify, and locate objects in water using sound waves. Sonar systems can be used in defense and civilian applications. Military applications include using underwater sound for depth detection, navigation, ship and submarine detection, ranging, tracking, underwater communications, mine detection, and guidance and control. Civilian applications include using underwater sound for depth detection, navigation, object location such as fish finding, bottom topographic mapping, underwater beacons, wave-height measurement, underwater imaging, telemetry and control, underwater communications, ship handling and docking, anti-stranding alerts for ships, and vessel velocity measurement.
A typical active sonar system includes a transmitter to generate sound waves and a receiver to sense reflected sound waves. The transmitter includes a transducer that generates sound waves and the receiver includes a transducer commonly referred to as a hydrophone that receives reflected sound waves. A short burst of energy, referred to as a sonar pulse, is generated by the transmitter. The sonar pulse travels to a target object and is reflected by the target object. The reflected sonar pulse is received by the hydrophone and the sonar system measures the time between the transmitted sonar pulse and the received reflected sonar pulse to determine the distance to the object. Often, each sonar pulse is transmitted, reflected, and received before transmitting another sonar pulse.
Typically, a substantial number of transmissions are needed to enable integration of the reflected sonar pulses and to accurately determine the distance to an object. Transmitting and receiving a substantial number of sonar pulses can be a time consuming process. Also, transmitting a substantial number of sonar pulses may give away the transmitters position, which is unacceptable in some military applications. Other problems encountered include high false alarm rates, inaccuracies, and false measurements. These problems may be due to transmission reverberations being received by the hydrophone and interpreted as reflected sonar pulses or sonar pulses bouncing from the bottom to the surface and back to the bottom, in double and triple bounces, before being received by the hydrophone.
For these and other reasons there is a need for the present invention.